It's super lightweight and superficial even in full. It's just not a large paper and takes a very superficial view of a lot of high level statistics. You can read through it in full in a few minutes and likely come to the same thought.

>This metric ignores the youth cohort

That's very very significant. They are not looking at population pyramids holistically at all. They are just focusing on part of the pyramid. Are there lots of people >65 compared to those between 16 and 65?

Now here's something to consider. If a population has very few children but many elderly they may actually have a great ratio of working/not-working. This study won't see this at all. Merely, look lots of elderly and they're doing great!!

I suspect the reality may well be that the most successful economies have offset the extra costs of more elderly with far far fewer children. So the elderly are indeed a burden as you'd expect but we're offsetting it with fewer children.

I'd also point out that I'm not convinced the arbitrary cutoff of >65 is correct since western governments are all pushing for retirement ages well above that. As in the worst of the bubble in the population pyramids is yet to fully hit, many in that bubble are still working and the effects of below population sustainment birth rates is also yet to fully hit (we don't yet fully have the narrowest parts of the population pyramids sustaining the widest parts). When it does all hit though it could well be devastating and this really superficial study doesn't reassure me at all.